Multi-stage centrifugal blowers, compressors and the like



Jan. 13, 1959 K. D. MCMAHAN MULTI-STAGE CENTRIFUGAL BLOWERS, COMPRESSORS AND THE LIKE 2 Sheets-Sheet 1 Filed Feb. 5. 1953 I INVENTOR [[bzziamfl M MafiaiZ BY m ,W/

, AT'FORNEY Jan. 13, 1959 McMAHAN 2,868,440

MULTI-STAGE CENTRIF'UGAL BLOWERS, COMPRESSORS AND THE LIKE Filed Feb. 3, 1953 I 2 Sheets-Sheet 2 INVENTOR KenonZZM Maimn BY 0/7 GO; ATTORNE Y MULTI-STAGE CENTRIFUGAL BLOWERS, COMPRESSORS AND THE LIKE Kenton D. McMahan, Scotia, N. Y.

Application February 3, 1953, Serial No. 334,797

18 Claims. (Cl. 230-130) The present invention relates to multi-stage centrifugal blowers, compressors and the like.

A known type of multi-stage centrifugal blower has .a series of successive stage impellers on a common shaft, each stage having an axial suction intake or eye and a volute perimetric discharge imparting rotation to the gases gathered therein and forced therethrough. All of the stages but the last one has passages leading from the outlet of the volute of one stage to the axial suction intake of the succeeding stage.

Due to rotational velocity components, turbulences, undesired accelerations, eddies and vacuous pockets initiated or. maintained in the stream flow between the discharge of a volute of one stage and the intake of a succeeding stage, substantial loss of head is incurred, resulting in socalled interstage losses. These interstage losses are the main cause for the comparatively low overall performance and low etficiency of blowers of the general type described, and the reason why the use of such blowers has heretofore been limited to applications requiring low specific performance or low volume flow, where efliciency is not of major importance.

One general object of the present invention is to provide a new and improved multi-stage centrifugal blower, which although small and compact is of comparatively high specific performance and efficiency.

A more specific object of the invention is to provide a new and improved multi-stage centrifugal blower designed to nullify the rotational velocity components of the stream from one stage, to suppress formation of eddies and vacuous pockets in said stream and to create other stabilizing conditions tending to maintain streamline motion or flow affording smooth intake into the axial suction eye of the succeeding stage and corresponding reduction in interstage head losses.

In accordance with one feature of the invention, the discharge from the first stage of the blower is divided into two jets of equal magnitude but opposed directions and guided radially inwardly (i. e. along radial planes which include the axis of the stage impellers) in alignment along a radial center plane and in centered position across the eye of the next stage impeller, where they merge into a single stream. By this impact of the two opposed jets of equal magnitude, the rotational velocity components in the gases are effectively nullified, and the resulting stream deflected axially with substantially uniform axial velocity distribution and minimum of bend losses.

As another feature, the multi-stage centrifugal blower has an operating stage with a radial diffuser, a multiple outlet diffuser scroll and a flow restricting elbow leading from each scroll outlet and designed to direct the discharge from said outlet radially inward towards the suction eye of the next stage.

As a further feature, the multi-stage centrifugal blower has an interstage passage of area restricting design and with converging boundaries to suppress eddy formation and/ or vacuous pockets.

Various other objects, features and advantages of the.

stream in its passage from a discharge volute of one stage to the suction eye of the succeeding stage;

Fig. 5 is a fragmentary section of the multi-stage blower taken approximately along the lines 55 of Fig. 1 and showing the pattern of eddies in one of the volutes and in the interstage elbow; and

Fig. 6 is a section similar to that of Fig. 3 but showing a modified form of multi-stage blower embodying the present invention.

Referring to Figs. 1-5 of the drawings, there is shown a two-stage centrifugal blower 10, although as far as certain aspects of the invention are concerned, the blower may have any number of stages to assure any desired final discharge pressure. This blower 10 is shown driven by a high frequency induction motor 11, suitably mounted on elastic supports 12 and 13, and having a shaft 14. The blower 10 comprises a casing 15 through which the motor shaft 14 extends axially, and two stages of blade impellers 16 and 17 in said casing, keyed or otherwise affixed to said sh aft.

The first stage impeller 16 has an axial entrance orifice 20 through which the intake air or other gas to be compressed is delivered. Around the impeller 16 is'a first stage radial diffuser 21 of expanding area serving to convert velocity head to pressure head. Around the diffuser 21 are two similar perimetric involute discharge scrolls 22 and 22a for gathering the air from the diffuser and forcing it therethrough by its rotation-for discharge towards the next compressing stage.

The casing 15 is desirably substantially elliptic to afford compactness and to converge the boundaries of the interstage elbows, as will be made more apparent, and the twin discharge volutes 22 and 22a follow closely along their outer peripheries the elliptic contour of said casing and are disposed in opposed relationship with respect to the axis of the blower, with their outlets 24 and 24a respectively, located diametrically opposite each other near the major axis of said casing. The outer side wall 26 of the casing 15 is shown forming the outer side walls of the volutes 22 and 22a, as Well as the outer side wall of the diffuser chamber 21. The opposite inner side wall 27 of each volute 22 and 22a slants divergently away from its outer side wall 26 along its length, from its inlet end where said inner side volute wall 27 is substantially in registry with the inner side Wall 28 of the diffuser chamber 21, to its outlet 24 or 24a. The discharge volutes 22 and 22a will thereby have respective cross-sectional areas expanding towards their respective outlets 24 and 24a and will serve thereby not only as discharge conduits but also as diffusers to convert velocity head into pressure head.

The air or gas jets J and I discharged from the volute outlets 24 and 24a are diverted along curved streamlined courses by means of elbows 35 and 3511 respectively, merging into respective interstage passageways 36 and 36a leading to an axial suction eye 37 defining the inlet to the second stage impeller 17. The gas: jets J and I as they are discharged from the outlets 24 and 24a of the respective volutes 22 and 22a are diverted along the inner elliptic wall of the casing 15 forming the entry parts of the elbows 35 and 35a and then baffled radially inwardly into the interstage passageways 36 and 36a respectively by main directing vanes 38 and 38a. These main directing vanes 38 and 38a have curved radially outer sections 40 and 40a, substantially continuing in contour from the peripheral wall of the casing 15 and defining therewith, the outer curved walls of the elbows 35 and 35a respectively and have fiat extensions 41 and 41a respectively,

The elbow and interstag-e passage structures comprise angular walls 42 and 42a having respective leg sections 43 and 43a extending substantially parallel to the axis of the blower and connecting into the side casing wall 26 and having respective leg sections 44 and 44a, the radially outer parts of which extend substantially radially towards the axis of the blower and at right angles thereto,

Axially facing the wall section 44 and substantially parallel thereto is a wall 46 fixed at its radially outer end to a radial partition wall 47 separating the two compressor stages, and defining with said wall section and with the main deflecting vane 38, the elbow 35 and the interstage passage 36. Similarly, a wall (not shown) facing the wall section 44;: and fixed at its radially outer end to the radial. partition wall 47 defines with said wall section and with the main, deflecting vane 38a, the elbow 35a and the interstage passage 36a.

At their radially inner ends, the walls 42 and 46 are formed with a 90 bend 50, to impart a corresponding configuration to the int-erstage passageway 36, so that the outlet of said passageway is turned towards the suction eye 37 of the second impeller 17 in a direction parallel to the axis of said impeller. Similarly, the wall 42a and the wall (not shown) corresponding to the wall 46 and axially facing said wall 42a are formed with a 90 bend for turning the outlet stream from the interstage passageway 36a in a direction parallel to the axis of the impellers 1'6 and 17.

The main deflecting vane 38 forms the outer boundary for the jet J discharged from the volute 22. To define the inner boundary for the jet J, there is provided a shorter vane 55 facing the main deflecting vane 38 near the suction eye 37 of the second stage impeller 17. The two opposed vanes 55 and 38 have their fiat sections extending parallel to a radial plane therebetween passing through the axis of the impellers 16 and 17 and located in centered position with respect to said plane, and at their discharge ends 57 converge with streamline curvature towards the axis of said impellers. These vanes 55 and 3 3 are desirably bank-ed at 58 to direct the sides of the jet I along said vanes towards the suction eye 37, as the jet rounds the terminal ends of said vanes.

Similarly, the main deflecting vane 32:: forms the outer boundary for the jet 1 discharged from the volute 22a and a shorter vane 55a facing said main deflecting vane near the suction eye 37 of the second stage impeller 17 forms the inner boundary for said jet. The two opposed vanes 55a and 35a have their flat sections extending parallel to a radial plane t'herebetween of the impeller axis and located in centered position with respect to said plane, and at their discharge ends 57a converge with streamline curvature towards said axis. These vanes 55a and 3&1 are banked at 53a to direct the sides of the jet 1' along said vanes towards the suction eye 37, as the jet rounds the terminal ends of said vanes.

To prevent the formation of eddies and to suppress those which originate in the volutes 22 and 22a, the cross-sectional areas of the jets J and I at the discharge ends of the respective elbows 35 and 35a at 60 and 66a where they merge into their respective interstage passageways 36 and 36a must not be greater than the discharge areas of the corresponding volutes 22 and 22a, and should desirably be approximately 20% less.

Also, it is desirable that the area of the second stage suction eye 37 be smaller than the combined area of the streams .l and J at the discharge ends of the elbows 35 and 3551, where they merge into their respective interstage passageways 36 and 36a. More specifically, this suction eye area should desirably be 20% less than this combined stream area.

Moreover, the width of the jets J and I in the interstage passageways 36 and 36a between the vanes 38 and 55 and between the vanes 38a and 55a, before convergence of said vanes at their discharge ends, should be greater than the diameter of the second impeller suction eye 37 and desirably 40% greater.

Also, the main deflecting vanes 38 and sea at the inlet ends of the elbows 35 and 35a where they join into the side casing wall 26, are desirably offset at sections 62 and 62a obliquely with respect to said wall and to the main body of said vanes. The resulting change in the contour of the boundary of the jets J and J in the elbows 35 and 35a serves to suppress eddies in the elbows 35 and 35a originating elsewhere and to prevent the initiation of other eddies and of vacuous pockets in said elbows. Converging the boundaries of the jets J and J in the elbows 35 and 35a by gradual reduction in the eifective cross-sectional areas respectively of said elbows and sizing the streams J and J with respect to the dimensions of the impeller suction eye 37, in the manner described, also assists in maintaining streamline motion and smooth intake into the suction eye 37.

In the embodiment of the invention shown in Fig. 3, midway between the inner and outer boundaries of the jet I along the center of pressure of said jet is an intermediate equalizing vane 65 for assisting in the proper distribution of the gases throughout the elbow, and midway between the inner and outer boundaries of the jet J along the center of pressure of said jet J is a similar intermediate equalizing vane 65a. These intermediate vanes 65 and 65a are curved at their outer sections 66 and 66a respectively to follow the general contour of the jets I and l, as they are guided into the elbows 35 and 35a, and have inner sections 67 and 67a respectively extending radially of the impeller axis. Where these intermediate vanes 65 and 65a join into the side casing wall 26 at sections 68 and 6&1, they are offset obliquely with respect to said wall and to the main body of said vanes, to change the general flow contours of the jet layers'as they pass along said intermediate vanes. This change in contour serves to suppress eddies in these jet layers, as in the case of the otisets 62 and 62a in the main deflecting vanes 38 and 33a.

The gases passing through the second impeller suction eye 37 are drawn into the second impeller 17, where they undergo a second stage of compression. The second stage is shown similar to the first stage as far as radial diffuser and twin volute discharge is concerned. However, as far as certain aspects of the invention are concerned, any type of second stage scroll or discharge design maybe employed.

The gases from the second stage are shown discharged along an annular plenum chamber 79 surrounding the motor ill. A ventilating fan 71 connected to the shaft 14 of the motor 11 draws air through the body of the motor '11 and especially around the coils to cool the motor and discharges into the chamber 70. As far as the blower features are concerned, the motor may be of any type ventilated or unventilated.

In the operation of the blower of the present invention, the compressed gases as they are discharged along the volutes 22 and 22a in the first stage, generate eddies along the surfaces of volutes, the eddies along the opposite walls of the volutes rotating in opposite directions, as shown by the arrows in Figs. 4 and 5. As the jets J and J are discharged from the volutes 22 and 22a into the elbows 35 and 35a, the converging solid boundaries presented to the jets by the elliptic casing 15 cause the eddies on the outer side of the jets and along said casing to be suppressed. As the remnants of these eddies travel along the offset sections 62 and 62a of the main directing vanes 33 and 38a and along the offset setcions 68 and 68a of the intermediate vanes 65 and 65a, the changes stacks rotating in opposite directions.

ot contours afforded by these offsets further suppress the eddies, as shown in Fig. 4. The eddies on the inner sides of the volutes 22 and 22a, as they leave the volutes travel between said volutes and the short vanes 55 and 55a. The jets I and J have no solid boundaries on the sides thereof between the volutes 22 and 22a and the short vanes 55 and 55a, so that the eddies on these sides lose activity, as they travel towards these vanes.

Some eddies may be initiated or maintained in the jet I along the solid walls 42 and 46 of the interstage passageway 36 and in the jet I along the corresponding solid walls of the interstage passageway 36a, as shown in Fig.

4, but these rotate in opposite directions. Similarly, whatever eddies may survive or may be initiated along the vanes 38 and 38a and along the vanes 55 and 55a are arranged in opposite stacks, with the eddies in opposed Even if these stacking eddies should persist as they enter the field of action of the second impeller 17, the blades from this impeller will first slice a section of a stack of eddies rotating in one direction and then a stack of eddies rotating in the opposite direction. The fluid friction between the sliced eddies rotating in opposite directions will cause the rotational energy of the eddies, to be quickly dissipated before reaching the diffuser of the second stage.

The jets J and J of equal magnitude, are directed in the interstage' passageways 36 and 36a radially inwardly along substantially straight line and in centered position with respect to the impeller axis, so that the center of pressure of the two jets are exactly opposed to each other. During the movement of the jets I and I along the elbows 35 and 35a and along the interstage passageways 36 and 36a, eddies originating outside of these flow conduits are suppressed and the formation of other eddies in these conduits are inhibited, as already described. As the two jets J and I meet and merge at the entrance to the suction eye 37 of the second impeller stage, and are deflected in .a radial direction into said suction eye, the rotational velocity components in said jets are effectively nullified, and smooth intake into the second stage assured, with substantially uniform axial velocity distribution. Interstage losses will thereby be reduced to a minimum.

It has been found that the performance of a multistage blower of the improved type described, equals substantially the calculated performance based upon the performance of the respective stages tested separately. The blower will have a high specific volume and will have utility, especially where the gas pressure to be developed is at least 2 ounces per square inch.

In the modified construction of Fig. 6, the main deflecting vanes 38b and 38c are foreshortened at their radially inner ends and the shorter vanes corresponding to the vanes 55 and 55a in the construction of Figs. 15 are omitted. There are, therefore, no converging vanes at the radially inner ends of the interstage passageways 36b and 36c where the two opposed jets I and I meet. However, the forces produced by the impact of the two opposingjets J and I will serve the purpose of converging vanes at the radially inner ends of the interstage passageways 36b and 36c but will not be effective in suppressing the eddies in the effective manner performed by the con struction of Figs. 15.

Also, in the modified construction of Fig. 6 the intermediate vanes 65 and 65a are omitted, although it is more desirable to provide such vanes to assist in the uniform distribution of the gases through the passageways leading to the suction eye 37 of the second impeller stage.

While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not to be limited thereto but is to be construed broadly and restricted solely by the scope of the appended claims.

Whatis claimed is: a a 1 l. A multi-stage centrifugal machine for compressing gas or vapor, comprising a casing, two successive stage units in said casing comprising two successive coaxial stage impellers respectively, inlet means for the earlier stage unit, the later stage unit having an axial inlet suction eye and outlet means for the discharge from the later stage unit, means for creating from the discharge from the impeller of the earlier stage unit two jets of equal magnitude, and guide wall means for directing said two jets in opposed directions radially inwardly towards said suction eye in alignment along a radial center plane and in centered positions over the axis of the impellers, each of said jets being separate, distinct and circumferentially remote y from any other jet, whereby each of said two jets is circumferentially discontinuous and whereby substantially balanced impact of the two jets is eifected as they meet in the vicinity of said suction eye and substantially smooth axial deflection of said two jets into said suction eye is effected as they merge into a single stream. i

2. A multi-stage centrifugal machine as defined in claim 1, wherein the jet creating means comprises twin discharge volutes with respective outlets in substantially diametrically opposite positions with respect to the axis of the impellers.

3. A multistage centrifugal machine as defined in claim 1, wherein the jet creating means comprise twin discharge volutes provided with respective outlets disposed near the perimeter of said casing and located in substantially diametrically opposite positions in relation to the axis of the impellers.

4. A multi-stage centrifugal machine as defined in claim 1, wherein the jet creating means comprise twin discharge volutes with respective outlets in substantially diametrically opposite positions with respect to the axis of the impellers, and wherein said guide wall means define a pair of twin passageways on opposite sides of the axis of the impellers extending in alignment along the radial center plane and provided with respective inlet ends and with respective discharge ends which extend to regions near the front of said suction eye, and wherein said guide wall means include a pair of curved elbows having inlet ends communicating with the volute outlets respectively and having outlet ends connecting into the inlet ends of said passageways respectively.

5. A multi-stage centrifugal machine as defined in claim 4, wherein said elbows have converging boundaries to inhibit the initiation of eddies therein and to suppress eddies initiated elsewhere.

6. A multi-stage centrifugal machine for compressing gas or vapor, comprising a casing, two successive stage units in said casing comprising two successive coaxial stage impellers respectively, inlet means for the earlier stage unit, the later stage unit having an axial inlet suction eye and outlet means for the discharge from the later stage unit, means for receiving the discharge from the impeller of the earlier stage unit and for dividing said discharge into two jets of equal magnitude, saidrec'eiving and dividing means having two outlets for said jets re spectively disposed in substantially diametrically opposite positions with respect to the axis of the impellers and located at equal distances radially from said suction eye, the outlet sections of said receiving and dividing means extending substantially along the perimeter of the casing to eject the jets therefrom in corresponding directions, and guide wall means for diverting the jets from their courses as they are discharged from the outlets of said discharge receiving and dividing means and. for deflecting them in opposed directions radially inwardly towards said suction eye in alignment along a radial center plane and in centered positions over the axis of the impellers, each of said jets being separate, distinct and circumferentially remote from any other jet, whereby each of said two jets is circumferentially discontinuous, and whereby substantially balanced impact of the two jets is effected as they meet in the vicinity of said suction eye and substantially smooth axial deflection of said jets into said suction eye is effected as they merge into a single stream.

7. A multi-stage centrifugal machine for compressing gas or vapor, comprising an elliptic casing, two successive stage units in said casing comprising two successive coaxial stage impellers respectively, inlet means for the earlier stage unit, the later stage unit having an axial inlet suction eye and twin discharge volutes for the impeller of the earlier stage unit extending along said casing about the axis of the impellers in substantial conformity with vthe elliptic curvature of said casing and having respective outlets in substantially diametrically opposite positions along the major axis of said casing, and guide wall means for directing the discharges from the outlets of said volutes towards said suction eye as two opposed jets of equal magnitude and for causing said jets to flow radially inwardly in alignment along a radial center plane and in centered positions over the axis of the impellers, said jets being free of any clrcumferentially contiguous jets, whereby each of said two jets is circumferentially discontinuous, and whereby substantially balanced impact of the two jets is effected as they meet in the vicinity of said suction eye and substantially smooth axial deflection of said jets into said suction eye is effected as they merge into a single stream.

8. A multi-stage centrifugal machine as described in claim 7, wherein said guide wall means define a pair of twin passageways on opposite sides of the axis of the impellers extending in alignment along the center radial plane and provided with respective inlet ends and with respective discharge ends which extend to regions near the front of said suction eye, and wherein said guide wall means include a pair of elbows having inlet ends communicating with the volute outlets respectively and having outlet ends connecting into the inlet ends of said passageways respectively, said elbows having outer curved walls conforming with the curved elliptic walls respectively of said casing and extending from the outlets of said vo-lutes respectively.

9. A multi-stage centrifugal machine as described in claim 2, wherein the guide wall means for eachof the two jets comprises a main deflecting vane having a curved inlet section forming the curved outer wall of an elbow, said vane extending from a region in front of the outlet of the corresponding volute towards a region near the front of said suction eye, the inner side of said elbow facing said curved vane section and located near said volute outlet being free of solid boundaries.

10. A multi-stage centrifugal machine as described in claim 2, wherein the wall guide means for each of the two jets comprises a main deflecting vane defining one boundary of the latter jet and having a curved inlet end section in front of the outlet of the corresponding volute serving as an outer curved wall for the bend of the latter jet as the latter jet is discharged from the latter volute outlet, said vane having a discharge section near the front of said suction eye, and a shorter vane facing the discharge section of said main deflecting vane near the front of said suction eye, to define the opposite boundary of the latter jet near the front of said suction eye, and extending short of the bend of the jet course near the corresponding volute outlet, said vanes at their discharge ends curving towards the suction eye.

11. A multi-stage centrifugal machine as described in claim 2, wherein the guide wall means for each of the two jets comprises a main deflecting vane defining one boundary of the latter jet and having a curved inlet end section in front of the outlet of the corresponding volute forming the outer curved wall of an elbow for the latter jet, a vane facing said main deflecting vane and defining the opposite boundary of the latter jet, and an intermediate equalizing vane extending along said elbow substantially midway between the boundaries thereof and located along substantially the center of pressure of the latter jet, for assistingin the proper distribution of the gases throughout the elbow.

12. A multi-stage centrifugal machine as described in claim 4, wherein each of said elbows comprises a pair of facing side walls, and a main deflecting vane between said walls having a curved section defining'the outer curved wall of said elbow, the part of said curved vane section connecting into one of said side walls being offset with respect to the main body of said curved vane section, and with respect to the latter side wall, to change the flow contour of the jet as it passes over the offset and thereby to suppress eddies in the latter jet.

13. A multi-stage centrifugal machine as described in claim 4, wherein eachof said elbows comprises a pair of facing side walls, and a main deflecting vane between said sidewalls having a curved section defining the outer curved walls of said elbow, the part of said curved vane section connecting into one of said side walls being offset with respect to the main body of said curved vane section, and with respect to the latter side wall, to change the flow contour of the jet as it passes over the offset and thereby to suppress eddies in the latter jet, and an intermediate curved equalizing vane between said side walls extending along said elbow substantially midway between the boundaries thereof and located along substaneye is smaller than the combined cross-sectional areas of the two jets.

15. A multi-stage centrifugal machine as described in claim 1, wherein the cross-sectional area of said suction eye is about 20% smaller than the combined cross-sectional areas of the two jets.

16, A multi-stage centrifugal machine as described in claim 1, wherein the guide Walls means comprise a pair of deflecting vanes for each of the two jets defining opposed outer boundaries of the latter jet, one of said vanes being curved at its inlet end to form the outer curved wall of an elbow, the distance between said vanes in planes at right angles to said radial center plane and in the vicinity of said suction eye being greater than the diameter of said suction eye.

17. A multi-stage centrifugal machine as described in claim 16, wherein the distance between said vanes in planes at right angles to said radial center plane and in the vicinity of said suction eye is about 40% greater than the diameter of said suction eye.

18. A multi-stage centrifugal machine as described in claim 4, wherein each elbow and the corresponding passageway are entirely free from solid boundaries on the inner concave side of the elbow and along the corresponding side of said passageway, and thereof are entirely open on said side.

References Cited in the file of this patent UNITED STATES PATENTS 

